Tipar Objeto no TypeScript: Interface e Type

// Interface - a forma clássica
interface User {
  id: number;
  name: string;
  email: string;
  age?: number; // opcional
  readonly createdAt: Date; // não pode mudar
}

const user: User = {
  id: 1,
  name: "Carlos",
  email: "carlos@dev.com",
  createdAt: new Date(),
};
// user.createdAt = new Date(); // ERRO! readonly

// Type alias pra objetos
type Product = {
  id: number;
  name: string;
  price: number;
  category: "eletronico" | "roupa" | "comida";
};

// Inline type - pra objetos usados uma vez só
function printUser(user: { name: string; age: number }) {
  console.log(`${user.name} tem ${user.age} anos`);
}

// Index signature - chaves dinâmicas
interface Dictionary {
  [key: string]: string;
}

const translations: Dictionary = {
  hello: "olá",
  goodbye: "tchau",
  thanks: "obrigado",
};

// Record - atalho elegante pra index signature
type StatusMap = Record<string, boolean>;

const features: StatusMap = {
  darkMode: true,
  notifications: false,
  beta: true,
};

// Record com chaves limitadas
type Role = "admin" | "user" | "guest";
type Permissions = Record<Role, string[]>;

const perms: Permissions = {
  admin: ["read", "write", "delete"],
  user: ["read", "write"],
  guest: ["read"],
};

// Objetos aninhados com tipos separados
interface Address {
  street: string;
  city: string;
  state: string;
  zipCode: string;
}

interface Company {
  name: string;
  address: Address;
  employees: number;
}

interface Employee {
  id: number;
  name: string;
  company: Company;
  address: Address; // reutiliza o mesmo tipo
  metadata: Record<string, unknown>; // dados extras flexíveis
}

// Partial - todas as props viram opcionais
type UpdateUser = Partial<User>;
// Pick - só algumas props
type UserPreview = Pick<User, "id" | "name">;
// Omit - todas menos algumas
type UserWithoutEmail = Omit<User, "email">;